Normally one should be using Matplotlib ≥ 3.x to avoid issues as below, since they added better backend autodetection in modern Matplotlib. Older Matplotlib installs that used QT4Agg may give error message

ImportError: No module named ‘PySide’

While the best fix is to update your Python install to use current versions of Matplotlib and associated libraries, if that is not feasible, a manual workaround follows:

Install QT 5: conda install pyqt and add to matplotlibrc the line

backend: qt5agg

Note that one should generally not be using PySide anymore.

Obsolete

Do not use this fix anymore as it’s for obsolete Python versions.

pip install pyside

This may require the prerequisites:

apt install libxext-dev python-qt4 qt4-dev-tools build-essential